Pneumatic tire

ABSTRACT

In a pneumatic tire, a cord spacing between an axially outer cord layer and an axially inner cord layer such as: a turnup portion and a main portion of a carcass ply; or a bead reinforcing cord layer and a carcass ply turnup portion, is increased from the radially inside to the outside of the tire to improve the durability of the bead portion.

The present invention relates to a pneumatic tire having an improvedbead structure capable of improving the durability.

In general, heavy duty tires for trucks, buses and the like are providedwith big bead portions to withstand heavy loads.

In Japanese Patent 724291, however, in order to improve bead durability,a pneumatic tire having relatively small bead portions was proposed. Inthis proposition, the rubber on the axially inside of the carcass shownin FIG. 9 by broken line is reduced in the volume. And on the radiallyoutside of a bead core (c), a turnup portion (d1) and main portion (d2)of a carcass ply adjoin each other to extend parallel with each other.

In order to further improve durability of this bead structure, thepresent inventors studied mechanism of possible bead damage, and it wasfound that

a stress on the radially outer end (e) of the turnup portion (d1)increases as it approaches the maximum tire section width position, and

the stress is liable to cause small cracks (initial cracks) around theouter end (e), and

the small cracks grow radially inwards through between the turnupportion (d1) and main portion (d2) to cause separation failure.

It is therefore, an object of the present invention to provide apneumatic tire, especially a heavy duty radial tire, in which theabove-mentioned small cracks around the radially outer ends of thecarcass ply turnup portions are prevented.

According to the present invention, a pneumatic tire comprises a treadportion, a pair of sidewall portions, a pair of bead portions each witha bead core therein, and at least one pair of an axially outer cordlayer and an axially inner cord layer each extending radially outwardlyfrom each bead portion, wherein the axially outer cord layer isterminated at a radial height not more than 50% of the section height ofthe tire, and the axially inner cord layer extends radially outwardlybeyond the radially outer end of the axially outer cord layer, and acord spacing between the axially outer cord layer and the axially innercord layer decreases radially inwardly from the radially outer end ofthe axially outer cord layer.

Embodiments of the present invention will now be described in detail inconjunction with the accompanying drawings.

FIG. 1 is a cross sectional view of a pneumatic tire according to thepresent invention showing a basic tire structure.

FIG. 2 is an enlarged cross sectional view of an example of the beadportion thereof showing an arrangement of various rubber components.

FIG. 3 is an enlarged cross sectional view showing another arrangementsimilar to that in FIG. 2.

FIG. 4 is a cross sectional view showing a reinforcing cord layercombinable with the basic tire structure.

FIG. 5 is a cross sectional view showing another reinforcing cord layercombinable with the basic tire structure.

FIG. 6 and FIG. 7 are schematic cross sectional views showingmodifications of the reinforcing cord layer shown in FIG. 5.

FIG. 8 is a cross sectional view showing a prior art.

In the drawings, tire 1 according to the present invention is a radialtire for trucks and buses.

The tire 1 comprises a tread portion 2, a pair of sidewall portions 3, apair of bead portions 4 each with a bead core 5 therein, a carcass 6extending between the bead portions 4, and a belt disposed radiallyoutside the carcass 6 in the tread portion 2.

The carcass 6 comprises at least one ply 6A of rubberized cords 6 carranged radially at an angle of from 70 to 90 degrees with respect towith respect to the tire equator C, and extending between the beadportions 4 through the tread portion 2 and sidewall portions 3, andturned up around the bead core 5 in each bead portion from the axiallyinside to the outside of the tire to form a pair of turnup portions 6 band a main portion 6 a therebetween. For the carcass cords 6 c, steelcords or organic fiber cords, e.g. nylon, rayon, polyester, aromaticpolyamide and the like can be used. In the example shown in FIG. 1, thecarcass 6 is composed of a single ply 6A of steel cords arranged atsubstantially 90 degrees. The carcass profile is designed to minimizeits change from the non-inflated condition to the inflated condition,and the carcass ply turnup portion is disposed adjacently to the mainportion to decrease stress at the carcass ply turnup end.

Preferably, the topping rubber 6 g for the carcass cords 6 c has a 100%modulus of from 37 to 47 kgf/sq.cm (3628 to 4610 kPa).

The belt comprises a breaker 7 and optionally a band (not shown).

The breaker 7 comprises at least two cross plies of parallel cords. Forthe breaker cords, steel cords or organic cords, e.g. rayon, nylon,aromatic polyamide, nylon and the like can be used.

In FIG. 1, the breaker 7 is composed of four plies: a radially innermostfirst ply 7A of steel cords laid at an angle of from 50 to 70 degreeswith respect to the tire equator C, and second, third and fourth plies7B, 7C and 7D each of steel cords laid at an angle of not more than 30degrees with respect to the tire equator C.

The bead core 5 is a coil of a steel wire 5 w, and the outer surfacethereof is covered with a thin wrapping rubber. Apart from steel wire,organic material such as aromatic polyamide cords may be used in thebead core 5.

In FIG. 1, the bead core 5 is formed into a hexagonal cross sectionalshape, and a radially inner side 5 i thereof inclines almost parallelwith the bead base so that the radially inner side 5 i inclines at aninclination angle almost same as the bead seat J1 of a standard rim J,that is, about 15 degrees with respect to the tire axial direction.

Here, the standard rim is the “standard rim” specified in JATMA, the“Measuring Rim” in ETRTO, the “Design Rim” in TRA or the like. In thiscase, therefore, the standard rim J is a 15-degree-taper center-droprim. Besides, the standard pressure is the “maximum air pressure” inJATMA, the “Inflation Pressure” in ETRTO, the maximum pressure given inthe “Tire Load Limits at Various Cold Inflation Pressures” table in TRAor the like. The standard load is the “maximum load capacity” in JATMA,the “Load Capacity” in ETRTO, the maximum value given in theabove-mentioned table in TRA or the like.

If not specifically mentioned, the heights referred hereafter mean aradial height measured radially from the bead base line BL under a statein which the tire is mounted on a standard rim and inflated to astandard presser but loaded with no tire load. The tire section height His a radial height from the bead base line BL to the tire radiallyoutermost point of the tire. The bead base line BL is a tire axial lineextending at a radial position corresponding to the diameter of thestandard rim.

Each of the bead portions 4 is provided between the carcass ply turnupportion 6 b and main portion 6 a with a rubber bead apex 8, the beadapex 8 extending radially outwardly from the bead core 5 and taperingtowards its radially outer end. The height (ha) of the outer end 8 t ofthe bead apex 8 is 6 to 31%, preferably 8 to 22%, more preferably 8 to14% of the tire section height H. (in this embodiment about 11%) Thebead apex 8 has an axially outer surface which is curved concavely. But,the an axially inner surface thereof is substantially straight andinclines substantially parallel with the carcass main portion 6 a. Thebead apex preferably has a JIS-A-hardness of from 60 to 99 degrees, anda 100% modulus of from 14 to 120 kgf/sq.cm (1372 to 11768 kPa).

The radially outer end 6 t of the turnup portion 6 b is positionedradially outward of the radially outer end 8 t of the bead apex 8, butradially inwards of the maximum tire section width point M. The height(h0) of the outer end 6 t is in the range of from 15 to 50%, preferably20 to 40% of the tire section height H. (in this embodiment about 32%)

The cord spacing (t) between the carcass cords 6 c in the turnup portion6 b and those in the main portion 6 a decreases from the bead core 5towards the outer end 8 t of the bead apex 8, and the cord spacing (t)becomes a minimum value (tmin) near the outer end 8 t.

The minimum value (tmin) is set in the range of from 0.15 to 7.0 timespreferably 0.15 to 5.0 times, more preferably 0.15 to 4.5 times, stillmore preferably 0.5 to 3.5 times, more preferably 0.8 to 2.5 times thediameter D of the carcass cords 6 c.

A region X (hereinafter parallel region X) in which the cord spacing (t)is the minimum value (tmin) continues for a certain length. The parallelregion X exists in a radial height range between 1.1 times and 1.5 timesthe height (ha) of the bead apex 8, at least partially. Preferably, theparallel region X extends over the whole of the range. In any case, itis possible that the parallel region X extends outside this range.

In the parallel region X, the ratio (tmin/h) between a height (h) andthe cord spacing (t=tmin) at the height (h) is set in the range of from0.01 to 0.07, preferably 0.02 to 0.05, wherein the units of the heightand cord spacing are the same.

A region Y (hereinafter, variable region Y) in which the cord spacing(t) gradually increases from the minimum value (tmin) towards theradially outside is formed to extend radially outwardly from theradially outer end of the parallel region X. The variable region Y isformed in a radial height range between 0.4 times and 1.0 times theheight (h0) of the turnup portion. This means that the variable regionmay extends from 0.4 to 1.0 times h0, or from 0.5 to 1.0 times h0, orfrom 0.8 to 1.0 times h0, for example. Preferably, the variable region Yextends to the radially outer end 6 t of the turnup portion 6 b. Inother words, the gradual increase of the cord spacing (t) continues tothe radially outer end 6 t as shown in FIG. 1. However, it may bepossible that the variation of the cord spacing in the variable region Ydecreases near the radially outer end 6 t of the turnup portion 6 b andas a result a substantially parallel region is formed.

To gradually increase the cord spacing (t), it is possible to employ: alinear increase—for example, the cord spacing (t) increases inproportion to the height (h) from the bead base line BL (thus t/h issubstantially constant)—; and a non-linear increase—for example, thecord spacing (t) increases in proportion to the square of the height (h)(thus t/h{circumflex over ( )}2 is substantially constant).

In case of a linear increase, the ratio (t/h) between a height (h) andthe cord spacing (t) at the height (h) is set at a substantiallyconstant value in the range of from 0.01 to 0.07, preferably 0.02 to0.05, more preferably 0.03 to 0.05. If the ratio (t/h) is less than0.01, it becomes difficult to control initial cracks at the outer end 6t. If the ratio (t/h) is more than 0.07, the rubber between the turnupportion 6 b and main portion 6 a is liable to deteriorate by heat due tosharing stress during running.

The cord spacing (t) reaches to a maximum value (tmax) at the radiallyouter end 6 t of the turnup portion 6 b. The maximum value (tmax) is setin the range of from 0.5 to 9.0 times, preferably 1.0 to 6.0 times, morepreferably 1.5 to 4.5 times the diameter D of the carcass cords 6 c,which is usually 1.3 to 3.0 times the minimum value (tmin).

By providing such variable region Y, initial cracks can be controllednear the turnup end 6 t and near the bead apex end 8 t and thedurability of the bead portion 4 can be improved.

As shown in FIG. 2,3 and 5, the carcass ply turnup portion 6 b iscovered with an insulation rubber 10 made of a rubber compound differentfrom a sidewall rubber 11 and a chafer rubber 12.

The insulation rubber 10 comprises an axially inner-part 10 a disposedon the axially inside of the turnup portion 6 b, an axially outer part10 b disposed on the axially outside of the turnup portion 6 b, and aradially outer tapered part 10 c.

The axially inner part 10 a extends from the turnup end 6 t to the beadapex end 8 t to provide the above-mentioned cord spacing (t).

The axially outer part 10 b has a substantially uniform thickness andextends from the turnup end 6 t to a position radially inside the beadcore 5. Preferably, the thickness (te) at the outer end 6 t is set at atleast 1 mm.

The radially outer tapered part 10 c extends radially outwardly from theturnup end 6 t to a radial position spaced apart from the turnup end 6 tby a radial distance of at least 60 mm preferably at least 75 mm toimprove the adhesion to the sidewall rubber 11.

The insulation rubber 10 has a 100% modulus of from 15 to 47 kgf/sq.cm(1470 to 4606 kPa).

On the axially outside of the insulation rubber 10, there are disposedthe sidewall rubber 11 defining the outer surface of the sidewallportion 3, and a chafer rubber 12 spliced with the sidewall rubber 11and defining a outer surface contacting with the wheel rim J. Thesidewall rubber 11 has a 100% modulus of from 10 to 20 kgf/sq.cm (980 to1961 kPa), and the chafer rubber 12 has a 100% modulus of from 55 to 71kgf/sq.cm (5394 to 6963 kPa).

In FIG. 2, the insulation rubber 10 is made of one kind of rubbercompound having a 100% modulus of from 37 to 47 kgf/sq.cm (3628 to 4610kPa).

FIG. 3 shows another example of the insulation rubber 10 which is madeof a packing rubber P1 having a 100% modulus of from 15 to 47 kgf/sq.cm(1470 to 4610 kPa) and an insulating rubber P2 having a 100% moduluswhich is higher than the packing rubber P1 and in the range of from 37to 47 kgf/sq.cm (3628 to 4610 kPa). The packing rubber P1 is disposedaxially inside the turnup end 6 t and extends between the axially innerpart 10 a and radially outer tapered part 10 c. The radial distance fromthe outer end 6 t to the radially outer end or the radially inner end isat least 10 mm preferably at least 15 mm.

The insulating rubber P2 forms other than the packing rubber part P1,namely, as shown in FIG. 3, the whole of the axially outer part 10 b, anaxially outside portion of the tapered part 10 c, and a major portion ofthe axially inner part 10 d extending from its radially inner end.

The axially outer surface of the packing rubber P1 is covered with theinsulating rubber P2 not to contact with the sidewall rubber 11.

Therefore, movements of the turnup end 6 t can be suitably controlled bythe relatively high modulus of the insulating rubber P2. The relativelylow modulus of the packing rubber P2 can absorb movements of theinsulating rubber P2 and turnup portion 6 b as one. Thus, the insulationrubber 10 can insulate the outer end 6 t from movements of the sidewallrubber 11 and make it possible to further increase theseparation-preventing effect.

In case of a tubeless type, the tire 1 is further provided with an innerliner 9 which extends over the inner surface S of the tire.

The inner liner 9 is made of a butyl-rubber-base rubber compound whichcontains at least 60, preferably at least 90 parts by weight ofhalogenated butyl rubber with respect to 100 parts by weight of rubbermaterial. For the rest, diene rubber such as butadiene rubber andstyrene-butadiene rubber and natural rubber can be used. But, regularbutyl rubber is preferably used because of its excellent airtightnessand excellent adhesiveness to diene rubber used in the carcass toppingrubber. Further, it prevents the halogenated butyl rubber fromdeteriorating or hardening by build-up heat during running. In additionto the rubber materials, the inner liner rubber is compounded fromvarious additives: reinforcing agent such as carbon black; processingagent such as oil; retarder such as magnesia oxide, mercaptobenzothiazyl disulfide (MBTS); accelerator such as hydrozincite;vulcanizing agent such as sulfur; and the like.

The following Table 1 shows examples of such compound.

TABLE 1 Compound 1 2 3 4 5 6 Rubber material (parts by weight)Halogenated 65 80 90 100 70 95 butyl Regular butyl 35 20 10 0 0 0Natural rubber 0 0 0 0 30 5 Additive (phr) Carbon black 60 60 60 60 6060 Process oil 10 10 10 10 10 10 Stearic acid 2 2 2 2 2 2 Magnesia oxide0.5 0.5 0.5 0.5 0.5 0.5 MBTS 1.5 1.5 1.5 1.5 1.5 1.5 Hydrozincite 3 3 33 3 3 Sulfur 0.5 0.5 0.5 0.5 0.5 0.5 Air perme- 0.61 0.60 0.60 0.60 1.000.65 ability at 80 deg. C. (× 10{circumflex over ( )}⁹ cc-cm/sq · cm.sec · cmHg) Rheometer test Scorch time 7.5 5.1 4.6 4.0 (min.) 90% flowtime 126.0 110.3 100.1 86.5 (min.) Maximum 24.4 26.5 28.3 30.1 torque(pound · inch) Adhesiveness 7.0 7.8 8.3 8.2 to carcass (kgf/cm)

The inner liner 9 has a 100% modulus in the rage of from 5 to 20kgf/sq.cm (490 to 1960 kPa).

Usually, the thickness Tb of the inner liner 9 is substantially constantfrom bead to bead. But, it is possible that a part in a specific regionZ is thicker than the rest. This region Z is defined as extendingradially outwardly and inwardly from the carcass turnup end 6 t alongthe main portion 6 a by a distance K equal to the maximum section widthBW of the bead core 5. At least in this region Z, the rubber thicknessTb is set in the range of from 1.0 to 4.5 times preferably 1.5 to 3.0times the diameter D of the carcass cord 6 c.

As a result, decrease in the cord strength and adhesive strength withrubber due to permeated moisture in the tire can be prevented toeffectively prevent the initial cracks.

If the thickness Tb is less than 1.0 times the diameter D, it isinsufficient for preventing the moisture permeation, and the cordstrength and adhesion with rubber decrease. Further, the initial cracksare liable to be promoted. If the thickness Tb is more than 4.5 timesthe diameter D, the steering stability is deteriorated, and the weightand material cost increase, and fuel consumption increases.

In the examples shown in FIGS. 2 and 3, in order to prevent undulationsof the inner liner 9 during vulcanization and to further improve theadhesion between the inner liner 9 and the carcass 6, a rubber layer 16is disposed between the inner liner 9 and carcass 6. The 100% modulusthereof is in the range of 27 to 45 kgf/sq.cm (2646 to 4410 kPa) andlower than the carcass cord topping rubber 6 g.

Further, in order to improve the bead portion in the resistance tochafing which is sometimes caused in the heavy duty tire, it is possibleto provide the basic structures shown in FIGS. 1, 2 and 3 with areinforcing cord layer 13 shown in FIG. 4.

The reinforcing cord layer 13 is composed of a single ply of reinforcecords laid at an angle in the range of from 30 to 90 degrees, preferable30 to 60 degrees with respect to the circumferential direction of thetire.

In case of heavy duty tires, steel cords are preferably employed, butorganic fiber cords, e.g. aromatic polyamide, aliphatic polyamide andthe like can be employed.

The reinforcing cord layer 13 has a main part 14 disposed along theaxially outer surface of the turnup portion 6 b, and an axially inwardlyextending part 15 on the radially inside of the bead core. The radiallyouter end 14 t of the main part 14 is disposed in a radial height range(A) between the radially innermost point Ci of the bead core 5 and aposition which is radially outwardly spaced apart from the radiallyoutermost point Co of the bead core 5 by a radial distance equal to themaximum section width BW of the bead core 5. The axially inwardlyextending part 15 is ended in a range between a straight line M and anaxial line N. The straight line M is drawn from the center of gravity Cpof the bead core 5 on its cross sectional shape toward the radiallyinside of the bead core 5 normally to the direction of the maximumsection width of the bead core 5, which direction is almost parallelwith the bead bottom face. The axial line N is drawn axially inwardlyfrom the outer end 6 t of the turnup portion 6 b. Thus, the axiallyinwardly extending part 15 can be made higher than the main part 14contrary to the example shown. If the end 15 t of the axially inwardlyextending part 15 is positioned axial outside the line M or radiallyoutside the line N, separation from the carcass ply tends to occur.

The cord spacing (tf) between the cords of the reinforcing cord layer 13and the cords 6 c of the carcass ply 6A is set in the range of from 0.15to 4.5 times, preferably 0.5 to 3.5 times, more preferably 0.8 to 2.5times the diameter D of the carcass cord 6 c by disposing a rubber layertherebetween, If the cord spacing (tf) is less than 0.15 times thecarcass cord diameter D, a separation failure is liable to occur betweenthe reinforcing cord layer 13 and the carcass 6. If more than 4.5 times,as the thickness of the chafer rubber 12 under the bead core decreases,cord exposure and ply separation which greatly decrease the durabilitybecome liable to occur in the bead base, and further the tire becomeshard to be mounted on a wheel rim.

Incidentally, this reinforcing cord layer 13 can be used in combinationwith such a structure which is the substantially same as explained abovebut the variable region Y is omitted. Thus, only the parallel region Xwith the minimum cord spacing (tmin) is formed. In this case, the lengthof the parallel region X measured therealong is set in the range of from0.5 to 5.0 times, preferably 1.0 to 4.0 times, more preferably 2.0 to4.0 times the maximum section width BW of the bead core 5.

In a pneumatic tire of a tube type, the above-explained inner liner 9may be omitted, without changing other components.

When a pneumatic tire is mounted on a wheel rim without a tube, arelatively high rim flange is usually employed. Accordingly, a largeamount of frictional heat is generated during running because the beadportion rubs against the rim flange. The bead rubber is therefore liableto harden and deteriorate by the heat, and as a result, cracks areoccurred on the surface of the bead portion. The cracks easily grow intothe inside of the tire and cause a separation of the turnup portion fromthe surrounding rubber. This type of damage is called “chafing”.

In case of a heavy duty tire of a tube type, it is preferable that thebead apex 8 is made of a relatively hard rubber in comparison with thetubeless type: and the ratio (t/h) is a substantially constant value offrom 0.02 to 0.03. Further, in order to reinforce the bead portion andto improve the resistance to chafing which is sometimes caused in heavyduty tires of the tube type, it is preferable that each bead portion 4is provided with a reinforcing cord layer 20 on the axially outside ofthe turnup portion 6 b as shown in FIG. 5.

The reinforcing cord layer 20 is composed of a single ply of cords 20 c(steel cords or organic fiber cords) laid at an angle of from 30 to 90degrees, preferably 30 to 60 degrees with respect to the circumferentialdirection of the tire and rubberized with a topping rubber. The radiallyouter end 21 thereof is positioned at a height F in the range of from0.15 to 1.0 times, preferably 0.15 to 0.80 times, more preferably 0.20to 0.60 times, still more preferably 0.25 to 0.50 times the height h0 ofthe turnup portion 6 b. The reinforcing cord layer 20 extends radiallyinwardly to the maximum section width line PC of the bead core at least.The maximum section width line PC is a straight line drawn along thedirection of the maximum section width of the bead core 5 or a directionparallel to the bead seat of the wheel rim, passing the center of thebead core. If the outer end 21 is disposed at a position lower than 0.15times the height h0, the bead-rigidity-increasing effect decreases, andit becomes difficult to control the chafing. If the outer end 21 is atposition higher than 1.0 times the height h0, a large stressconcentrates on the outer end 21 when the sidewall portion 3 is largelydeformed and damages tend to occur in this part. If the inner end 22 ofthe reinforcing cord layer 20 does not extend to the line PC, it isdifficult to fully reinforce a region in which chafing is liable tooccur.

The cord spacing (j) between the reinforce cords 20 c of the reinforcingcord layer 20 and the carcass cords 6 c of the turnup portion 6 b is setas follows. In a radial height range V between 50% and 100% of theheight F of the reinforcing cord layer 20, the cord spacing (j)gradually increases towards the radially outside of the tire.(Hereinafter this region is called “second variable region 25.”) Thesecond variable region 25 extends at least 70%, preferably 100% of theregion V. To gradually increase the cord spacing (j), a linear increaseor non-linear increase explained in relation to the above-mentionedvariable region Y can be used. Thus, for example, the ratio (j/f)between a height (f) and the cord spacing (j) at the height (f) is setat a substantially constant value in the range of from 0.01 to 0.13,preferably 0.01 to 0.10, more preferably 0.02 to 0.09. If the ratio(j/f) is less than 0.01, the rubber between the reinforcing cord layer20 and turnup portion 6 b is not provided with a necessary thickness,and initial cracks and destruction of rubber are liable to occur nearthe outer end 21 of the reinforcing cord layer 20. If the ratio (j/f) ismore than 0.13, the thickness of rubber between the reinforcing cordlayer 20 and turnup portion 6 b excessively increased, and the outer endof the reinforcing cord layer 20 approaches to a region where a largecompressive strain occurs and the chafing-preventing effect decreases.

Therefore, initial cracks between the reinforcing cord layer 20 andturnup portion 6 b effectively prevented and the separation and chafingcan be controlled over a long time.

A part of the reinforcing cord layer 20 extending radially inwardly fromthe radially inner end of the second variable region 25 is disposedadjacently to the carcass ply turnup portions 6 b and in parallelthereto. (Hereinafter, second parallel region 26)

In FIG. 5, the second parallel region 26 extends to the radially innerend 22 of the reinforcing cord layer 20 which end is located axiallyoutside the bead core 5. In this region 26, the ratio (j/f) is set inthe range of from 0.01 to 0.08, more preferably 0.02 to 0.07.

FIG. 6 and FIG. 7 show modifications of the reinforcing cord layer 20.

In FIG. 6, the radially inner end 22 of the reinforcing cord layer 20 islocated at a position near the bead toe on the radially inside of theabove-mentioned line PC and axially inside the bead core 5.

In FIG. 7, the reinforcing cord layer 20 is turned up around the beadcore 5 towards the axially inside and the turner up portion extendsradially outwardly along the axially inner surface of the carcass mainportion 6 a. In this case, it is preferable that the end 22 ispositioned radially inward of the outer end 8 t of the bead apex 8.

In the second variable region 25, an insulation rubber 29 is disposedbetween the reinforcing cord layer 20 and the carcass turnup portion 6b. And the insulation rubber 29 extends radially outwardly beyond theradially outer end 21. The insulation rubber 29 has a 100% modulus offrom 14 to 65 kgf/sq.cm (1372 to 6374 kPa), preferably 20 to 50kgf/sq.cm (1961 to 4903 kPa), more preferably 37 to 47 kgf/sq.cm (3628to 4610 kPa).

The reinforcing cord layer 20 is combined with the above-mentionedcarcass structure defining both the parallel region X and variableregion Y as shown in FIGS. 1, 2, 3 and 5. It is however possible thatthe reinforcing cord layer 20 is combined with such a carcass structurethat the variable region Y is omitted. Thus, only the parallel region Xwith the minimum cord spacing (tmin) is defined as shown in FIG. 4.

The reinforcing cord layer 20 (and also 13) is a single ply structure,and in the examples shown in the figures, no further cord layer isdisposed along the outer surface of the reinforcing cord layer.

The present invention is suitably applied to heavy-duty tires such astruck/bus tires, but it may be applied to passenger-car tires,light-truck tires, motorcycle tires and the like.

Comparison Tests

Test tires having the basic structure shown in FIG. 1 were made andtested for durability to compare with the prior art tire shown in FIG.8.

In the durability test, each test tire was run on a tire test drum untilany visible damage occurred, and the running time was measured. The testresults are shown in Table 2. The tire weights are also indicated inTable 2 using an index based on Prior art tire 1 being 100. The largerthe value, the heavier the tire weight.

Test tire: 11R22.5 14PR tubeless-type heavy-duty radial tire Wheel rimsize: 8.25 × 22.5 Tire pressure: 1000 kPa Speed: 20 km/h Load: 9000 kgfMax. running distance: 10000 km Carcass Number of ply 1 Cord steel (3 ×0.17 + 7 × 0.20) diameter D = 0.9 mm Cord count 40/5 cm (under beadcore) Cord angle 90 degrees to Tire equator Topping rubber 100% modulus= 42 kgf/sq · cm Belt Number of ply 4 Cord steel (3 × 0.20 + 6 × 0.35)Cord count 26/5 cm Cord angle +67, +18, −18, −18 dgrees to tire equatorInsulation rubber 100% modulus = 41 kgf/sq · cm

TABLE 2 Tire Prior. 1 Ex. 1 Ex. 2 Ex. 3 Ref. 1 Ref. 2 Ref. 3 Ref. 4 Ex.4 Turnup portion Height h0 (mm) 70 70 70 70 70 70 70 70 70 Cord spacingt tmax (mm) 1.2 3.0 3.0 3.0 3.0 1.2 0.6 22 3.0 tmin (mm) 1.2 1.2 1.2 1.23.0 3.0 0.1 12 1.2 tmin/D 1.3 1.3 1.3 1.3 3.3 3.3 0.1 13.3 1.3 Variableregion t/h — 0.04 0.04 0.03-0.04 — — 0.003-0.009 0.3 0.03-0.04 Extendingrange (h/h0) — 0.38-1.0 0.42-1.0  0.57-1.0  — — 0.57-1.0  0.57-1.0 0.57-1.0  Parallel region Extending range (h/h0) 0.43-1.0  0.36-0.380.39-0.42 0.43-0.57 0.43-1.0  — 0.43-0.57 0.43-0.57 0.43-0.57 Extendingrange (h/ha) 1.1-2.5 1.01-1.04  1.1-1.16  1.1-1.43 1.1-2.5 —  1.1-1.43 1.1-1.43  1.1-1.43 Bead apex Height ha (mm) 28 25 25 25 28 28 28 28 25ha/h0 0.40 0.35 0.35 0.35 0.4 0.4 0.4 0.4 0.35 Insulation rubber 10Height of tapere part (mm) — — — — — — — — 96 Thickness te (mm) — — — —— — — — 1.5 Durability 100 103 108 110 97 60 70 90 150 Tire weight 100100 100 100 102 105 95 120 100

Further, test tires having the structure shown in FIG. 5 were made andtested for the durability and resistance to chafing.

Durability test: Same as above.

Chafing resistance test: When the running distance was reached to 8000km in the drum durability test, the tire was checked for the number ofcracks and the degree of deformation caused by chafing.

The test results are indicated in Table 3 using an index based. Thelarger the index, the better the performance.

Tire 10.00R20 14PR tube-type heavy-duty radial tire Wheel rim size 7.50× 20 Carcass Number of ply 1 Cord steel (3 × 0.2 + 7 × 0.23) diameter D= 0.9 mm Cord count 38/5 cm (under bead core) Cord angle 90 degrees totire equator Topping rubber 100% modulus = 42 kgf/sq · cm Belt Number ofply 4 Cord steel (3 × 0.20 + 6 × 0.35) Cord count 26/5 cm Cord angle+67, +18, −18, −18 degrees to tire equator Reinforcing cord layer Cordsteel (3 × 0.17 + 7 × 0.20 + WX0.15) Cord count 28/5 cm Cord angle 45degrees to circumferential direction

TABLE 3 Tire Prior. 2 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Structure FIG. 9FIG. 7 FIG. 5 FIG. 5 FIG. 5 FIG. 6 Height h0 (mm) 100 100 100 100 100100 Height ha (mm) 50 50 50 50 50 50 Height F (mm) — 40 40 33 101 40Height F′ (mm) — 49 8 8 8 51 Cord spacing t tmax (mm) 1.2 3.0 3.0 3.03.0 3.0 tmin (mm) 1.2 1.2 1.2 1.2 1.2 1.2 tmin/D 1.3 1.3 1.3 1.3 1.3 1.3Second Variable region Extending range (× F) 0.5-1.0 0.5-1.0 0.5-1.00.5-1.0 0.5-1.0 Cord spacing j Variable range (mm) —   1-3.5   1-3.5  1-3.5   1-3.5   1-3.5 Ratio (j/f) 0.05-0.09 0.05-0.09 0.05-0.090.05-0.09 0.05-0.09 Durability 100 108 110 106 90 110 Chafing resistance100 170 170 130 170 170 Tire weight 100 110 103 101 110 104

Further, test tires having the structure shown in FIG. 2 were made andsubjected to the above-mentioned drum durability test and a wetpressurizing test.

Wet pressurizing test was made as follows: First, a slash wound was madeon the inner surface of the tire; the tire was mounted on a wheel rim;200 cc water was injected thereinto; the tire is inflated with air to astandard pressure 1000 kPa; then the tire was run on a test drum underthe same conditions as the above-mentioned durability test whileinjecting another 200 cc water every 100 hours; and the running timeuntil any visible damage occurred was measured.

Further, the tires were subjected to a cut open inspection to check ifthe steel cords was rusted.

The results are indicated in Table 4 by an index based on Prior art tire1 being 100. The larger the indedx, the better the durability.

Test tire 11R22.5 14PR tubeless-type heavy-duty radial tire Wheel rimsize 8.25 × 22.5 Carcass Number of ply 1 Cord steel (3 × 0.2 + 7 × 0.23)Diameter D = 0.8 mm Cord count 36/5 cm (under the bead core) Cord angle90 degrees to tire equator Topping rubber 100% modulus = 42 kgf/sq · cmBelt Number of ply 4 Cord steel (3 × 0.20 + 6 × 0.35) Cord count 26/5 cmCord angle +67, +18, −18, −18 degrees to tire equator Insulation rubber10 100% modulus Ma = 41 kgf/sq · cm

TABLE 4 Tire Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ref. 5 Ref. 6 Ref. 7 Prior. 1Inner liner Halogenated butil 100 100 100 100 100 50 100 100 (parts byweight) Thickness Tb (mm) 1.0 4.5 2.8 2.8 0.9 4.6 2.8 0.9 Region Z4BW/4BW 4BW/4BW 4BW/4BW 4BW/4BW 4BW/4BW 4BW/4BW 0.9BW/0.9BW 5BW/8BWextending range (outside/inside) Carcass Turnup portion Height h0 (mm)70 70 70 70 70 70 70 70 tmax (mm) 3.0 3.0 3.0 3.0 3.0 3.0 3.0 1.2 tmin(mm) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Variable region Extending range(h/h0)  57-100  57-100  57-100  57-100  57-100  57-100  57-100 Parallelregion Extending range (h/h0) 43-56 43-56 43-56 43-56 43-56 43-56 43-56 43-100 Extending range (h/ha) 110-143 110-143 110-143 110-143 110-143110-143 110-143 110-250 Bead Apex 28 28 28 28 28 28 28 28 Height ha (mm)Weight 102 118 105 102 100 120 102 100 Durability 130 130 130 130 120120 120 100 Wet durability 130 170 170 150 100 90 100 100 Rust none nonenone none present present present present

What is claimed is:
 1. A pneumatic tire comprising: a tread portion, a pair of sidewall portions, a pair of bead portions each with a bead core therein, a carcass ply made of cords extending between the bead portions and turned up around the bead cores from the axially inside to the outside of the tire to form a turnup portion in each said bead portion and a main portion there between, a bead apex disposed between said main portion and the turnup portion in each said bead portion and tapering radially outwardly from the bead core to its radially outer end, at least one pair of an axially outer cord layer and an axially inner cord layer each extending radially outwardly from each bead portion, said axially outer cord layer terminating at a radial height not more than 50% of the section height of the tire, said axially inner cord layer extending radially outwardly beyond the radially outer end of said axially outer cord layer, a cord spacing between said axially outer cord layer and said axially inner cord layer decreasing radially inwardly from the radially outer end of the axially outer cord layer so that a minimum value (tmin) thereof is in the range of from 0.15 to 7.0 times the diameter of the carcass cords, said axially outer cord layer being the turnup portion of the carcass ply, the turnup portion sandwiched between an axially inner insulation rubber and an axially outer insulation rubber, each of the axially inner insulation rubber and axially outer insulation rubber having a 100% modulus higher than that of a sidewall rubber disposed axially outside the axially outer insulation rubber, and the 100% modulus of the axially outer insulation rubber being higher than the 100% modulus of the axially inner insulation rubber.
 2. The pneumatic tire according to claim 1, wherein said axially inner cord layer is said main portion of the carcass ply.
 3. The pneumatic tire according to claim 2, wherein a region in which said cord spacing has said minimum value (tmin) is formed at least partially in a height range between 1.1 times and 1.5 times a height (ha) of the bead apex from the bead base line.
 4. The pneumatic tire according to claim 1, wherein a region in which the ratio (t/h) of a height (h) from the bead base line and the cord spacing (t) thereat is a substantially constant value of from 0.01 to 0.07 is formed at least partially in a height range between 0.4 times and 1.0 times the height (h0) of the turnup portion from the bead base line.
 5. The pneumatic tire according to claim 1, wherein each said bead portion is provided with a reinforcing cord layer disposed axially outside the turnup portion, the reinforcing cord layer extends radially outwards but ends between a radial position of the radially innermost point (Ci) of the bead core and a radial position radially outwardly spaced apart from the radially outermost point (Co) of the bead core by a distance equal to the maximum section width (BW) of the bead core, the reinforcing cord layer extends radially inwards and then axially inwards along the carcass ply but does not extend radially outwardly beyond the radially outer end of the turnup portion. 